The present invention relates to a method of and apparatus for examining a diamond. For example, the invention may be used to test whether a diamond has had a layer of synthetic diamond deposited thereon. This is of particular importance in detecting whether the diamond comprises CVD diamond material and also in locating such material if present.
Over the years, a number of methods of synthesising diamond material have been developed. One of these methods is the chemical vapor deposition (CVD) technique, which is a low pressure technique involving deposition of synthetic diamond (referred to as CVD diamond material in this specification) onto a substrate from a gas.
The synthetic diamond material may be deposited on an uncut or part-worked natural diamond which is then worked, for example, into a round brilliant cut. Alternatively, the synthetic diamond coating may be deposited onto a fully fashioned brilliant stone after working of the stone. The thickness of such a synthetic diamond material layer may be very thin--it could be in the range from 1 .mu.m to 0.1 mm.
The value of a diamond is in part dependent upon its weight. Accordingly, synthetic diamond material such as CVD diamond material may be deposited onto natural gem diamonds, before or after cutting of the diamond, to increase the weight of the finished product. A diamond artificially enlarged by deposition of CVD diamond material is referred to in this specification as a "CVD/natural diamond doublet".
However, the value of a diamond also resides in its qualities of authenticity and uniqueness and in the fact that it is an entirely natural product. Thus, a diamond that has not been enlarged by deposition of synthetic diamond material has a value over a CVD/natural diamond doublet.
CVD diamond material may be deposited on a non-diamond or diamond substrate. In the latter case, the CVD diamond material can replicate the structure of the diamond substrate (referred to "homoepitaxial growth"). The CVD/natural diamond doublet produced can be identical in appearance, density and other common physical properties to an entirely natural diamond and there may be a problem in identifying such a CVD/natural diamond doublet.
It is an object of the present invention to provide a method of and apparatus for testing whether a diamond has had a layer of synthetic diamond deposited thereon.
It is desired that the apparatus should be simple and inexpensive and may be put into operation by a person with relatively little training. The method and apparatus should be capable of being operated reliably and consistently by a practised jeweller who has no training in laboratory gemological analysis.